For the purposes of reducing the weight and cost of many industrial parts, great efforts have hitherto been made to replace metal parts by plastic parts. Even in the fields of automotive parts and sliding members where impact resistance and durability are crucial, many plastic parts have been devised and used in practice. Known as the resin suited in such applications are polycarbonate resins, ABS resins, AS resins and polyamide resins, which are generally referred to as engineering plastics.
However, polycarbonate and ABS resins are short of sliding properties when used alone. Since they often fail to comply with the field requiring abrasion resistance, a further improvement in performance is needed. Also, polyamide and ABS resins have good sliding properties as such, but a further improvement in performance is needed in many fields.
To solve these problems, for example, JP-A 2002-363403 attempts to improve sliding properties by combining a polyamide resin with a modified polyolefin resin and a fluoroplastic or silicone lubricant. While it is essential to use a large amount of the modified olefin resin in combination with the polyamide resin, the modified olefin resin is less compatible, and interfacial separation is likely to occur. The fluoroplastic or silicone lubricant to be blended is also less compatible. Since the composition is liable to interfacial separation and difficult to mold, there is left room for further improvement.
JP-A 2003-082227 and JP-A 2004-107526 disclose polyamide compositions containing silicone. JP-A 2001-261919 discloses a sliding modifier which is obtained by graft polymerizing a vinyl polymer to a composite rubber composed of polyorganosiloxane rubber component and poly(alkyl(meth)acrylate) component to form a composite rubber-based graft copolymer and blending the composite rubber-based graft copolymer with a silicone oil or olefin oil. This sliding modifier is added to a thermoplastic resin or thermoplastic elastomer. However, since the silicone oil or olefin oil is blended, the composition is less compatible, liable to interfacial separation and difficult to mold.